Fibers and fabrics prepared from blends of homopolymers and copolymers

ABSTRACT

A fiber comprising a propylene polymer composition is disclosed. The composition comprises a resin blend of from about 75 to about 95 weight percent of a Ziegler-Natta or metallocene catalyzed isotactic polypropylene homopolymer, and from about 95 to about 75 weight percent of a metallocene catalyzed polypropylene copolymer. In this blend the copolymer component includes a comonomer in an amount from about 0.05 to about 25 weight percent, based on the copolymer. Non-woven fabrics prepared by thermally bonding the inventive fibers show improved tensile strengths, particularly machine direction, at comparable basis weights that are at least about 5 percent higher than those of fabrics prepared using identical preparation techniques but from the isotactic polypropylene homopolymer alone.

BACKGROUND OF THE INVENTION

1. Technical Field

This invention relates to the field of fibers and more specifically to the field of fibers and fabrics prepared from blends of polypropylene homopolymers and copolymers.

2. Background of the Art

Homopolymers and copolymers of polypropylene are typically polymerized in continuous polymerization reactors, such as, for example, loop reactors. To produce these polymers one or more monomer streams are generally introduced into the selected reactor and then circulated with an appropriate catalyst. Ziegler-Natta or metallocene catalysts may be employed. The resulting polymers may be subjected to appropriate purification and post-processing steps and then made into end products using conventional techniques such as injection molding and extrusion. These end products may include fibers, which may then be used to prepare woven and non-woven products.

Propylene polymer fibers and fabrics are widely used in many applications including twine, carpet, medical gowns and drapes, and diapers. The optimization of processing characteristics and properties of propylene based fibers and fabrics has been the subject of intense effort. When the fibers are used to form fabrics, specifically nonwoven fabrics, various methods of thermal bonding are employed. To accomplish this it is desirable to have high strength when bonding at the lowest possible temperatures. Unfortunately, many polypropylene fabrics exhibit relatively poor strength properties, and the resins used to prepare them may also present challenges relating to melt spinning and overall melt processing. It would therefore be desirable to have a means or method of providing propylene-based fabric and fibers with improved thermal bonding characteristics, softness and fabric strength properties which may be prepared from resins having desirable melt spinning and melt processing characteristics.

SUMMARY OF THE INVENTION

In one aspect, the invention is a fiber, spunbond fabric, or melt blown fabric including a polymer composition that includes a resin blend of from about 60 to about 99 weight percent of a Ziegler-Natta or metallocene catalyzed isotactic polypropylene homopolymer, and from about 1 to about 40 weight percent of a metallocene catalyzed propylene copolymer. The copolymer includes a comonomer in an amount from about 0.05 to about 25 weight (or higher) percent, based on the copolymer.

In another aspect, the invention is an article including a fiber prepared using a polymer composition that includes a resin blend of from about 60 to about 99 weight percent of a Ziegler-Natta or metallocene catalyzed isotactic polypropylene homopolymer, and from about 1 to about 40 weight percent of a metallocene catalyzed propylene copolymer. The copolymer includes a comonomer in an amount from about 0.05 to about 25 weight percent, based on the copolymer.

Another aspect of the invention is a thermally bonded non-woven fabric made using a fiber including a polymer composition including a resin blend of from about 75 to about 95 weight percent of a Ziegler-Natta or metallocene catalyzed isotactic polypropylene homopolymer, and from about 95 to about 75 weight percent of a metallocene catalyzed polypropylene copolymer. The copolymer includes a comonomer in an amount from about 0.05 to about 25 weight percent, based on the copolymer.

An aspect of the invention is an article including a thermally bonded non-woven fabric made using a fiber including a polymer composition including a resin blend of from about 75 to about 95 weight percent of a Ziegler-Natta or metallocene catalyzed isotactic polypropylene homopolymer, and from about 95 to about 75 weight percent of a metallocene catalyzed polypropylene copolymer. The copolymer includes a comonomer in an amount from about 0.05 to about 25 weight percent, based on the copolymer.

In still another aspect, the invention is a method for preparing a non-woven fabric, the method including melt spinning a polymer composition including a resin blend of from about 75 to about 95 weight percent of a Ziegler-Natta or metallocene catalyzed isotactic polypropylene homopolymer, and from about 95 to about 75 weight percent of a metallocene catalyzed propylene copolymer. The copolymer includes a comonomer in an amount from about 0.05 to about 25 weight percent, based on the copolymer. The method also includes forming a fiber and thermally bonding the fiber at a temperature of at least about 240° C.

DETAILED DESCRIPTION OF THE INVENTION

Disclosed herein are fibers and non-woven fabrics that may be prepared from a specific blend of metallocene catalyzed polypropylene copolymers and either metallocene catalyzed, or Ziegler-Natta catalyzed, isotactic polypropylene homopolymers. The blend may be in the form of discreet resin blends or in the form of in-situ reactor blends. The resin blend may exhibit good melt spinning processability for preparing fibers. These fibers may be used to form non-woven fabrics in particular, using conventional processes including the spunbond or carded staple process. In either of these processes, the result may be a fabric that exhibits improved tensile strength and other properties, particularly when compared to fabrics prepared using the same homopolymer alone. In other words, incorporation of a given proportion of a metallocene catalyzed copolymer in the starting resin improves the strength properties of the fiber and/or fabric when compared with the strength properties attained by the homopolymer alone.

The resin blend includes a major proportion of an isotactic polypropylene homopolymer and a minor proportion of a random copolymer. These polymers may each be prepared using any conventional polymerization method known or used in the art. Reactor types may include, for example, loop, slurry, continuous stirred tank, or other, and polymerization protocol and conditions may be determined accordingly, as are well known to those of ordinary skill in the art. Gas, slurry, solution phase, and high pressure autoclave processes are all contemplated hereby. For example, a slurry polymerization process may be selected and will generally use pressures of from about 1 to about 100 atmospheres (about 0.1 to about 10 MPa) or greater, and temperatures from about 60° C. to about 150° C. In some embodiments the temperature is from about 50° C. to about 120° C. In such a polymerization a suspension of solid, particulate polymer is formed in a liquid or supercritical polymerization medium to which propylene (and, for the copolymer, a comonomer) and often hydrogen, along with a selected catalyst, are added. The liquid employed in the polymerization medium may be, for example, an alkane or cycloalkane. This medium desirably remains liquid under the conditions of polymerization and is also desirably relatively inert. For example, hexane or isobutene are often employed. Such polymerizations may be conducted in batch or continuous mode and may take place in one reactor or may be carried out in a series of reactors. The amount of time will depend upon the catalyst and reaction conditions. In general, propylene may desirably be homopolymerized or copolymerized for a time period sufficient to yield the intended final homopolymer or copolymer, typically from about 15 to about 120 minutes. In one embodiment the polymerization is continued for a time of from about 30 to about 60 minutes.

In the case of the copolymer, one or more comonomers is also added along with the propylene. In one embodiment the comonomer is a C₂ or C₄-C₁₆ compound, desirably C₂ or C₄-C₈. In another embodiment the comonomer is desirably ethylene (C₂). The comonomer level in the copolymer is desirably limited. In one embodiment the comonomer is desirably present in the final copolymer in an amount from about 0.05 to about 25 percent by weight of the copolymer. In another embodiment the comonomer is desirably present in an amount from about 1 to about 10 percent by weight of the final copolymer. Feed rate of the ethylene may be adjusted according to the rate of its incorporation into the copolymer under the selected polymerization conditions. Such adjustment will be easily within the skill of those in the art.

Hydrogen may be added to the polymerization system as a molecular weight regulator, depending upon the particular properties of the product desired and the specific catalyst used. When two catalysts having different hydrogen responses are used, the addition of hydrogen may affect the molecular weight distribution of the polymer product and may therefore be employed with the intent to tailor the molecular weight distribution for a specific purpose. This whole section is confusing, and maybe irrelevant. Narrow MWD is desired for spunbond fiber, either by metallocene catalsyst or vis-breaking via peroxide. I have not established the correlation between the MW of the blend resin with the host.

The catalyst that is desirably selected for preparing either just the copolymer, or for both the homopolymer and the copolymer, is a metallocene catalyst. Metallocene catalysts may be characterized generally as coordination compounds incorporating one or more cyclopentadienyl (Cp) groups (which may be substituted or unsubstituted, each substitution being the same or different) coordinated with a transition metal through pi bonding.

The Cp substituent groups may be linear, branched or cyclic hydrocarbyl radicals. The cyclic hydrocarbyl radicals may further form other contiguous ring structures, including, for example indenyl, azulenyl and fluorenyl groups. These additional ring structures may also be substituted or unsubstituted by hydrocarbyl radicals, such as C₁ to C₂₀ hydrocarbyl radicals.

A specific example of a metallocene catalyst is a bulky ligand metallocene compound generally represented by the formula: [L]_(m)M[A]_(n); where L is a bulky ligand, A is a leaving group, M is a transition metal and m and n are such that the total ligand valency corresponds to the transition metal valency. For example m may be from 1 to 3 and n may be from 1 to 3.

The metal atom “M” of the metallocene catalyst compound, as described throughout the specification and claims, may be selected from Groups 3 through 12 atoms and lanthanide Group atoms in one embodiment; and selected from Groups 3 through 10 atoms in a more particular embodiment, and selected from Sc, Ti, Zr, Hf, V, Nb, Ta, Mn, Re, Fe, Ru, Os, Co, Rh, Ir, and Ni in yet a more particular embodiment; and selected from Groups 4, 5 and 6 atoms in yet a more particular embodiment, and Ti, Zr, Hf atoms in yet a more particular embodiment, and Zr in yet a more particular embodiment. The oxidation state of the metal atom “M” may range from 0 to +7 in one embodiment; and in a more particular embodiment, is +1, +2, +3, +4 or +5; and in yet a more particular embodiment is +2, +3 or +4. The groups bound the metal atom “M” are such that the compounds described below in the formulas and structures are electrically neutral, unless otherwise indicated.

The bulky ligand generally includes a cyclopentadienyl group (Cp) or a derivative thereof. The Cp ligand(s) form at least one chemical bond with the metal atom M to form the “metallocene catalyst compound”. The Cp ligands are distinct from the leaving groups bound to the catalyst compound in that they are not highly susceptible to substitution/abstraction reactions.

Cp typically includes 7-bonded and/or fused ring(s) or ring systems. The ring(s) or ring system(s) typically include atoms selected from group 13 to 16 atoms, for example, carbon, nitrogen, oxygen, silicon, sulfur, phosphorus, germanium, boron, aluminum and combinations thereof, wherein carbon makes up at least 50% of the ring members. Non-limiting examples include cyclopentadienyl, cyclopentaphenanthrenyl, indenyl, benzindenyl, fluorenyl, tetrahydroindenyl, octahydrofluorenyl, cyclooctatetraenyl, cyclopentacyclododecene, phenanthrindenyl, 3,4-benzofluorenyl, 9-phenylfluorenyl, 8-H-cyclopent[a]acenaphthylenyl, 7-H-dibenzofluorenyl, indeno[1,2-9]anthrene, thiophenoindenyl, thiophenofluorenyl, hydrogenated versions thereof (e.g., 4,5,6,7-tetrahydroindenyl, or “H₄Ind”), substituted versions thereof, and heterocyclic versions thereof.

Cp substituent groups may include hydrogen radicals, alkyls, alkenyls, alkynyls, cycloalkyls, aryls, acyls, aroyls, alkoxys, aryloxys, alkylthiols, dialkylamines, alkylamidos, alkoxycarbonyls, aryloxycarbonyls, carbomoyls, alkyl- and dialkylcarbamoyls, acyloxys, acylaminos, aroylaminos, and combinations thereof. More particular non-limiting examples of alkyl substituents include methyl, ethyl, propyl, butyl, pentyl, hexyl, cyclopentyl, cyclohexyl, benzyl, phenyl, methylphenyl, and tert-butylphenyl groups and the like, including all their isomers, for example tertiary-butyl, isopropyl, and the like. Other possible radicals include substituted alkyls and aryls such as, for example, fluoromethyl, fluoroethyl, difluroethyl, iodopropyl, bromohexyl, chlorobenzyl and hydrocarbyl substituted organometalloid radicals including trimethylsilyl, trimethylgermyl, methyldiethylsilyl and the like; and halocarbyl-substituted organometalloid radicals including tris(trifluoromethyl)silyl, methylbis(difluoromethyl)silyl, bromomethyldimethylgermyl and the like; and disubstituted boron radicals including dimethylboron for example; and disubstituted Group 15 radicals including dimethylamine, dimethylphosphine, diphenylamine, methylphenylphosphine, Group 16 radicals including methoxy, ethoxy, propoxy, phenoxy, methylsulfide and ethylsulfide. Other substituents R include olefins such as but not limited to olefinically unsaturated substituents including vinyl-terminated ligands, for example 3-butenyl, 2-propenyl, 5-hexenyl and the like. In one embodiment, at least two R groups, two adjacent R groups in one embodiment, are joined to form a ring structure having from 3 to 30 atoms selected from the group consisting of carbon, nitrogen, oxygen, phosphorus, silicon, germanium, aluminum, boron and combinations thereof. Also, a substituent group R group such as 1-butanyl may form a bonding association to the element M.

Each anionic leaving group is independently selected and may include any leaving group, such as halogen ions, hydrides, C₁ to C₁₂ alkyls, C₂ to C₁₂ alkenyls, C₆ to C₁₂ aryls, C₇ to C₂₀ alkylaryls, C₁ to C₁₂ alkoxys, C₆ to C₁₆ aryloxys, C₇ to C₁₈ alkylaryloxys, C₁ to C₁₂ fluoroalkyls, C₆ to C₁₂ fluoroaryls, and C₁ to C₁₂ heteroatom-containing hydrocarbons and substituted derivatives thereof; hydride, halogen ions, C₁ to C₆ alkylcarboxylates, C₁ to C₆ fluorinated alkylcarboxylates, C₆ to C₁₂ arylcarboxylates, C₇ to C₁₈ alkylarylcarboxylates, C₁ to C₆ fluoroalkyls, C₂ to C₆ fluoroalkenyls, and C₇ to C₁₈ fluoroalkylaryls in yet a more particular embodiment; hydride, chloride, fluoride, methyl, phenyl, phenoxy, benzoxy, tosyl, fluoromethyls and fluorophenyls in yet a more particular embodiment; C₁ to C₁₂ alkyls, C₂ to C₁₂ alkenyls, C₆ to C₁₂ aryls, C₇ to C₂₀ alkylaryls, substituted C₁ to C₁₂ alkyls, substituted C₆ to C₁₂ aryls, substituted C₇ to C₂₀ alkylaryls and C₁ to C₁₂ heteroatom-containing alkyls, C₁ to C₁₂ heteroatom-containing aryls and C₁ to C₁₂ heteroatom-containing alkylaryls in yet a more particular embodiment; chloride, fluoride, C₁ to C₆ alkyls, C₂ to C₆ alkenyls, C₇ to C₁₈ alkylaryls, halogenated C₁ to C₆ alkyls, halogenated C₂ to C₆ alkenyls, and halogenated C₇ to C₁₈ alkylaryls in yet a more particular embodiment; fluoride, methyl, ethyl, propyl, phenyl, methylphenyl, dimethylphenyl, trimethylphenyl, fluoromethyls (mono-, di- and trifluoromethyls) and fluorophenyls (mono-, di-, tri-, tetra- and pentafluorophenyls) in yet a more particular embodiment; and fluoride in yet a more particular embodiment.

Other non-limiting examples of leaving groups include amines, phosphines, ethers, carboxylates, dienes, hydrocarbon radicals having from 1 to 20 carbon atoms, fluorinated hydrocarbon radicals (e.g., —C₆F₅ (pentafluorophenyl)), fluorinated alkylcarboxylates (e.g., CF₃C(O)O⁻), hydrides and halogen ions and combinations thereof. Other examples of leaving groups include alkyl groups such as cyclobutyl, cyclohexyl, methyl, heptyl, tolyl, trifluoromethyl, tetramethylene, pentamethylene, methylidene, methoxy, ethoxy, propoxy, phenoxy, bis(N-methylanilide), dimethylamide, dimethylphosphide radicals and the like. In one embodiment, two or more leaving groups form a part of a fused ring or ring system.

It is also possible that L and A may be bridged to one another. A bridged metallocene, for example may, be described by the general formula: XCp^(A)Cp^(B)MA_(n); wherein X is a structural bridge, Cp^(A) and Cp^(B) each denote a cyclopentadienyl group, each being the same or different and which may be either substituted or unsubstituted, M is a transition metal and A is an alkyl, hydrocarbyl or halogen group and n is an integer between 0 and 4, and either 1 or 2 in a particular embodiment.

Non-limiting examples of bridging groups (X) include divalent hydrocarbon groups containing at least one Group 13 to 16 atom, such as but not limited to at least one of a carbon, oxygen, nitrogen, silicon, aluminum, boron, germanium and tin atom and combinations thereof; wherein the heteroatom may also be C₁ to C₁₂ alkyl or aryl substituted to satisfy neutral valency. The bridging group may also contain substituent groups as defined above including halogen radicals and iron. More particular non-limiting examples of bridging group are represented by C₁ to C₆ alkylenes, substituted C₁ to C₆ alkylenes, oxygen, sulfur, R₂C═, R₂Si═, —Si(R)₂Si(R₂)—, R₂Ge═, RP═ (wherein “═” represents two chemical bonds), where R is independently selected from the group hydride, hydrocarbyl, substituted hydrocarbyl, halocarbyl, substituted halocarbyl, hydrocarbyl-substituted organometalloid, halocarbyl-substituted organometalloid, disubstituted boron, disubstituted Group 15 atoms, substituted Group 16 atoms, and halogen radical; and wherein two or more Rs may be joined to form a ring or ring system. In one embodiment, the bridged metallocene catalyst component has two or more bridging groups (X).

Other non-limiting examples of bridging groups include methylene, ethylene, ethylidene, propylidene, isopropylidene, diphenylmethylene, 1,2-dimethylethylene, 1,2-diphenylethylene, 1,1,2,2-tetramethylethylene, dimethylsilyl, diethylsilyl, methylethylsilyl, trifluoromethylbutylsilyl, bis(trifluoromethyl)silyl, di(n-butyl)silyl, di(n-propyl)silyl, di(i-propyl)silyl, di(n-hexyl)silyl, dicyclohexylsilyl, diphenylsilyl, cyclohexylphenylsilyl, t-butylcyclohexylsilyl, di(t-butylphenyl)silyl, di(p-tolyl)silyl and the corresponding moieties, wherein the Si atom is replaced by a Ge or a C atom; dimethylsilyl, diethylsilyl, dimethylgermyl and/or diethylgermyl.

In another embodiment, the bridging group may also be cyclic, and include 4 to 10 ring members or 5 to 7 ring members in a more particular embodiment. The ring members may be selected from the elements mentioned above, and/or from one or more of B, C, Si, Ge, N and O in a particular embodiment. Non-limiting examples of ring structures which may be present as or part of the bridging moiety are cyclobutylidene, cyclopentylidene, cyclohexylidene, cycloheptylidene, cyclooctylidene and the corresponding rings where one or two carbon atoms are replaced by at least one of Si, Ge, N and O, in particular, Si and Ge. The bonding arrangement between the ring and the Cp groups may be cis-, trans-, or a combination thereof.

The cyclic bridging groups may be saturated or unsaturated and/or carry one or more substituents and/or be fused to one or more other ring structures. If present, the one or more substituents are selected from the group hydrocarbyl (e.g., alkyl such as methyl) and halogen (e.g., F, Cl) in one embodiment. The one or more Cp groups which the above cyclic bridging moieties may optionally be fused to may be saturated or unsaturated and are selected from the group of those having 4 to 10 ring members, more particularly 5, 6 or 7 ring members (selected from the group of C, N, O and S in a particular embodiment) such as, for example, cyclopentyl, cyclohexyl and phenyl. Moreover, these ring structures may themselves be fused such as, for example, in the case of a naphthyl group. Moreover, these (optionally fused) ring structures may carry one or more substituents. Illustrative, non-limiting examples of these substituents are hydrocarbyl (particularly alkyl) groups and halogen atoms.

In one embodiment, the metallocene catalyst includes CpFlu Type catalysts (e.g., a metallocene incorporating a substituted Cp fluorenyl ligand structure) represented by the following formula: X(CpR¹ _(n)R² _(m))(FluR³ _(p)) wherein Cp is a cyclopentadienyl group, Fl is a fluorenyl group, X is a structural bridge between Cp and F¹, R¹ is a substituent on the Cp, n is 1 or 2, R² is a substituent on the Cp at a position which is proximal to the bridge, m is 1 or 2, each R³ is the same or different and is a hydrocarbyl group having from 1 to 20 carbon atoms with R³ being substituted on a nonproximal position on the fluorenyl group and at least one other R³ being substituted at an opposed nonproximal position on the fluorenyl group and p is 2 or 4.

In yet another aspect, the metallocene catalyst includes bridged mono-ligand metallocene compounds (e.g., mono cyclopentadienyl catalyst components). In this embodiment, the at least one metallocene catalyst component is a bridged “half-sandwich” metallocene catalyst. In yet another aspect of the invention, at least one metallocene catalyst component is an unbridged “half sandwich” metallocene.

Described another way, the “half sandwich” metallocenes above are described in U.S. Pat. No. 6,069,213, U.S. Pat. No. 5,026,798, U.S. Pat. No. 5,703,187, and U.S. Pat. No. 5,747,406, including a dimer or oligomeric structure, such as disclosed in, for example, U.S. Pat. No. 5,026,798 and U.S. Pat. No. 6,069,213, which are incorporated by reference herein.

Non-limiting examples of metallocene catalyst components consistent with the description herein include: cyclopentadienylzirconiumA_(n), indenylzirconiumA_(n), (1-methylindenyl)zirconiumA_(n), (2-methylindenyl)zirconiumA_(n), (1-propylindenyl)zirconiumA_(n), (2-propylindenyl)zirconiumA_(n), (1-butylindenyl)zirconiumA_(n), (2-butylindenyl)zirconiumA_(n), methylcyclopentadienylzirconiumA_(n), tetrahydroindenylzirconiumA_(n), pentamethylcyclopentadienylzirconiumA_(n), cyclopentadienylzirconiumA_(n), pentamethylcyclopentadienyltitaniumA_(n), tetramethylcyclopentyltitaniumA_(n), (1,2,4-trimethylcyclopentadienyl)zirconiumA_(n), dimethylsilyl(1,2,3,4-tetramethylcyclopentadienyl) (cyclopentadienyl)zirconiumA_(n), dimethylsilyl(1,2,3,4-tetramethylcyclopentadienyl)(1,2,3-trimethycyclopentadienyl)zirconiumA_(n), dimethylsilyl(1,2,3,4-tetramethylcyclopentadienyl)(1,2-dimethylcyclopentadienyl)zirconiumA_(n), dimethylsilyl(1,2,3,4-tetramethylcyclopentadienyl)(2-methylcyclopentadienyl)zirconiumA_(n), dimethylsilylcyclopentadienylindenylzirconiumA_(n), dimethylsilyl(2-methylindenyl)(fluorenyl)zirconiumA_(n), diphenylsilyl(1,2,3,4-tetramethylcyclopentadienyl)(3-propylcyclopentadienyl)zirconiumA_(n), dimethylsilyl (1,2,3,4-tetramethylcyclopentadienyl) (3-t-butylcyclopentadienyl)zirconiumA_(n), dimethylgermyl(1,2-dimethylcyclopentadienyl)(3-isopropylcyclopentadienyl)zirconiumA_(n), di-methylsilyl(1,2,3,4-tetramethylcyclopentadienyl)(3-methylcyclopentadienyl)zirconiumA_(n), diphenylmethylidene(cyclopentadienyl)(9-fluorenyl)zirconiumA_(n), diphenylmethylidenecyclopentadienylindenylzirconiumA_(n), isopropylidenebiscyclopentadienylzirconiumA_(n), isopropylidene(cyclopentadienyl)(9-fluorenyl)zirconiumA_(n), isopropylidene(3-methylcyclopentadienyl)(9-fluorenyl)zirconiumA_(n), ethylenebis(9-fluorenyl)zirconiumA_(n), mesoethylenebis(1-indenyl)zirconiumA_(n), ethylenebis(1-indenyl)zirconiumA_(n), ethylenebis(2-methyl-1-indenyl)zirconiumA_(n), ethylenebis(2-methyl-4,5,6,7-tetrahydro-1-indenyl)zirconiumA_(n), ethylenebis(2-propyl-4,5,6,7-tetrahydro-1-indenyl)zirconiumA_(n), ethylenebis(2-isopropyl-4,5,6,7-tetrahydro-1-indenyl)zirconiumA_(n), ethylenebis(2-butyl-4,5,6,7-tetrahydro-1-indenyl)zirconiumA_(n), ethylenebis(2-isobutyl-4,5,6,7-tetrahydro-1-indenyl)zirconiumA_(n), dimethylsilyl(4,5,6,7-tetrahydro-1-indenyl)zirconiumA_(n), diphenyl(4,5,6,7-tetrahydro-1-indenyl)zirconiumA_(n), ethylenebis(4,5,6,7-tetrahydro-1-indenyl)zirconiumA_(n), dimethylsilylbis(cyclopentadienyl)zirconiumA_(n), dimethylsilylbis(9-fluorenyl)zirconiumA_(n), dimethylsilylbis(1-indenyl)zirconiumA_(n), dimethylsilylbis(2-methylindenyl)zirconiumA_(n), dimethylsilylbis(2-propylindenyl)zirconiumA_(n), dimethylsilylbis(2-butylindenyl)zirconiumA_(n), diphenylsilylbis(2-methylindenyl)zirconiumA_(n), diphenylsilylbis(2-propylindenyl)zirconiumA_(n), diphenylsilylbis(2-butylindenyl)zirconiumA_(n), dimethylgermylbis(2-methylindenyl)zirconiumA_(n), dimethylsilylbistetrahydroindenylzirconiumA_(n), dimethylsilylbistetramethylcyclopentadienylzirconiumA_(n), dimethylsilyl(cyclopentadienyl)(9-fluorenyl)zirconiumA_(n), diphenylsilyl(cyclopentadienyl)(9-fluorenyl)zirconiumA_(n), diphenylsilylbisindenylzirconiumA_(n), cyclotrimethylenesilyltetramethylcyclopentadienyl-cyclopentadienylzirconiumA_(n), cyclotetramethylenesilyltetramethylcyclopentadienylcyclopentadienylzirconiumA_(n), cyclotrimethylenesilyl(tetramethylcyclopentadienyl)(2-methylindenyl)zirconiumA_(n), cyclotrimethylenesilyl(tetramethylcyclopentadienyl)(3-methylcyclopentadienyl)zirconiumA_(n), cyclotrimethylenesilylbis(2-methylindenyl)zirconiumA_(n), cyclotrimethylenesilyl(tetramethylcyclopentadienyl)(2,3,5-trimethylcyclopentadienyl)zirconiumA_(n), cyclotrimethylenesilylbis(tetramethylcyclopentadienyl)zirconiumA_(n), dimethylsilyl(tetra-methylcyclopentadieneyl)(N-tertbutylamido)titaniumA_(n), biscyclopentadienylchromiumA_(n), biscyclopentadienylzirconiumA_(n), bis(nbutylcyclopentadienyl)zirconiumA_(n), bis(n-do-decylcyclopentadienyl)zirconiumA_(n), bisethylcyclopentadienylzirconiumA_(n), bisisobutyl-cyclopentadienylzirconiumA_(n), bisisopropylcyclopentadienylzirconiumA_(n), bismethylcyclo-pentadienylzirconiumA_(n), bisnoxtylcyclopentadienylzirconiumA_(n), bis(n-pentylcyclo-pentadienyl)zirconiumA_(n), bis(n-propylcyclopentadienyl)zirconiumA_(n), bistrimethyl-silylcyclopentadienylzirconiumA_(n), bis(1,3-bis(trimethylsilyl)cyclopentadienyl)zirconiumA_(n), bis(1-ethyl-2-methylcyclopentadienyl)zirconiumA_(n), bis(1-ethyl-3-methylcyclopenta-dienyl)zirconiumA_(n), bispentamethylcyclopentadienylzirconiumA_(n), bispentamethylcyclopentadienylzirconiumA_(n), bis(1-propyl-3-methylcyclopentadienyl)zirconiumA_(n), bis(1-nbutyl-3-methylcyclopentadienyl)zirconiumA_(n), bis(1-isobutyl-3-methylcyclopentadienyl)zirconiumA_(n), bis(1-propyl-3-butylcyclopentadienyl)zirconiumA_(n), bis(1,3-n-butylcyclopentadienyl)zirconiumA_(n), bis(4,7-dimethylindenyl)zirconiumA_(n), bisindenylzirconiumA_(n), bis(2-methylindenyl)zirconiumA_(n), cyclopentadienylindenylzirconiumA_(n), bis(n-propylcyclopentadienyl)hafniumA_(n), bis(n-butylcyclopentadienyl)hafniumA_(n), bis(n-pentylcyclopentadienyl)hafniumA_(n), (n-propylcyclopentadienyl)(n-butylcyclopentadienyl)hafniumA_(n), bis[(2-trimethylsilylethyl)cyclopentadienyl]hafniumA_(n), bis(trimethylsilylcyclopentadienyl)hafniumA_(n), bis(2-n-propylindenyl)hafniumA_(n), bis(2-n-butylindenyl)hafniumA_(n), dimethylsilylbis(n-propylcyclopentadienyl)hafniumA_(n), dimethylsilylbis(n-butylcyclopentadienyl)hafniumA_(n), bis(9-n-propylfluorenyl)hafniumA_(n), bis(9-n-butylfluorenyl)hafniumA_(n), (9-npropylfluorenyl)(2-n-propylindenyl)hafniumA_(n), bis(1-n-propyl-2-methylcyclopentadienyl)hafniumA_(n), (n-propylcyclopentadienyl)(1-n-propyl-3-n-butylcyclopentadienyl)hafniumA_(n), dimethylsilyltetramethylcyclopentadienylcyclopropylamidotitaniumA_(n), dimethylsilyl-tetramethylcyclopentadienylcyclobutylamidotitaniumA_(n), dimethylsilyltetramethylcyclopentadienylcyclopentylamidotitaniumA_(n), dimethylsilyltetramethylcyclopentadienylcyclohexylamidotitaniumA_(n), dimethylsilyltetramethylcyclopentadienylcycloheptylamidotitaniumA_(n), dimethylsilyltetramethylcyclopentadienylcyclooctylamidotitaniumA_(n), dimethylsilyltetramethylcyclopentadienylcyclononylamidotitaniumA_(n), dimethylsilyltetramethylcyclopentadienylcyclodecylamidotitaniumA_(n), dimethylsilyltetramethylcyclopentadienylcycloundecylamidotitaniumA_(n), dimethylsilyltetramethylcyclopentadienylcyclododecylamidotitaniumA_(n), dimethylsilyltetramethylcyclopentadienyl(sec-butylamido)titaniumA_(n), dimethylsilyl(tetramethylcyclopentadienyl)(n-octylamido)titaniumA_(n), dimethylsilyl(tetramethylcyclopentadienyl)(n-decylamido)titaniumA_(n), dimethylsilyl(tetramethylcyclopentadienyl)(n-octadecylamido)titaniumA_(n), methylphenylsilyltetramethylcyclopentadienylcyclopropylamidotitaniumA_(n), methylphenylsilyltetramethylcyclopentadienylcyclobutylamidotitaniumA_(n), methylphenylsilyltetramethylcyclopentadienylcyclopentylamidotitaniumA_(n), methylphenylsilyltetramethylcyclopentadienylcyclohexylamidotitaniumA_(n), methylphenylsilyltetramethylcyclopentadienylcycloheptylamidotitaniumA_(n), methylphenylsilyltetramethylcyclopentadienylcyclooctylamidotitaniumA_(n), methylphenylsilyltetramethylcyclopentadienylcyclononylamidotitaniumA_(n), methylphenylsilyltetramethylcyclopentadienylcyclodecylamidotitaniumA_(n), methylphenylsilyltetramethylcyclopentadienylcycloundecylamidotitaniumA_(n), methylphenylsilyltetramethylcyclopentadienylcyclododecylamidotitaniumA_(n), methylphenylsilyl(tetramethylcyclopentadienyl)(sec-butylamido)titaniumA_(n), methylphenylsilyl(tetramethylcyclopentadienyl)(n-octylamido)titaniumA_(n), methylphenylsilyl(tetramethylcyclopentadienyl)(n-decylamido)titaniumA_(n), methylphenylsilyl(tetramethylcyclopentadienyl)(n-octadecylamido)titaniumA_(n), diphenylsilyltetramethylcyclopentadienylcyclopropylamidotitaniumA_(n), diphenylsilyltetramethylcyclopentadienylcyclobutylamidotitaniumA_(n), diphenylsilyltetramethylcyclopentadienylcyclopentylamidotitaniumA_(n), diphenylsilyltetramethylcyclopentadienylcyclohexylamidotitaniumA_(n), diphenylsilyltetramethylcyclopentadienylcycloheptylamidotitaniumA_(n), diphenylsilyltetramethylcyclopentadienylcyclooctylamidotitaniumA_(n), diphenylsilyltetramethylcyclopentadienylcyclononylamidotitaniumA_(n), diphenylsilyltetramethylcyclopentadienylcyclodecylamidotitaniumA_(n), diphenylsilyltetramethylcyclopentadienylcycloundecylamidotitaniumA_(n), diphenylsilyltetramethylcyclopentadienylcyclododecylamidotitaniumA_(n), diphenylsilyl(tetramethylcyclopentadienyl)(sec-butylamido)titaniumA_(n), diphenylsilyl(tetramethylcyclopentadienyl)(n-octylamido)titaniumA_(n), diphenylsilyl(tetramethyleyclopentadienyl)(n-decylamido)titaniumA_(n), diphenylsilyl(tetramethylcyclopentadienyl)(n-octadecylamido)titaniumA_(n) and derivatives thereof.

As used herein, the term “metallocene activator” is defined to be any compound or combination of compounds, supported or unsupported, which may activate a single-site catalyst compound (e.g., metallocenes, Group 15 containing catalysts, etc.) Typically, this involves the abstraction of at least one leaving group (A group in the formulas/structures above, for example) from the metal center of the catalyst component. The catalyst components of the present invention are thus activated towards olefin polymerization using such activators. Embodiments of such activators include Lewis acids such as cyclic or oligomeric polyhydrocarbylaluminum oxides and so called non-coordinating ionic activators (“NCA”), alternately, “ionizing activators” or “stoichiometric activators”, or any other compound that may convert a neutral metallocene catalyst component to a metallocene cation that is active with respect to olefin polymerization.

More particularly, it is within the scope of this invention to use Lewis acids such as alumoxane (e.g., “MAO”), modified alumoxane (e.g., “TIBAO”), and alkylaluminum compounds as activators, to activate desirable metallocenes described herein. MAO and other aluminum-based activators are well known in the art. Non-limiting examples of aluminum alkyl compounds which may be utilized as activators for the catalysts described herein include trimethylaluminum, triethylaluminum, triisobutylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum and the like.

Ionizing activators are well known in the art and are described by, for example, Eugene You-Xian Chen & Tobin J. Marks, Cocatalysts for Metal-Catalyzed Olefin Polymerization: Activators, Activation Processes, and Structure-Activity Relationships 100(4) CHEMICAL REVIEWS 1391-1434 (2000). Examples of neutral ionizing activators include Group 13 tri-substituted compounds, in particular, tri-substituted boron, tellurium, aluminum, gallium and indium compounds, and mixtures thereof (e.g., tri(n-butyl)ammonium tetrakis(pentafluorophenyl)boron and/or trisperfluorophenyl boron metalloid precursors). The three substituent groups are each independently selected from alkyls, alkenyls, halogen, substituted alkyls, aryls, arylhalides, alkoxy and halides. In one embodiment, the three groups are independently selected from the group of halogen, mono or multicyclic (including halosubstituted) aryls, alkyls, and alkenyl compounds and mixtures thereof. In another embodiment, the three groups are selected from the group alkenyl groups having 1 to 20 carbon atoms, alkyl groups having 1 to 20 carbon atoms, alkoxy groups having 1 to 20 carbon atoms and aryl groups having 3 to 20 carbon atoms (including substituted aryls), and combinations thereof. In yet another embodiment, the three groups are selected from the group alkyls having 1 to 4 carbon groups, phenyl, naphthyl and mixtures thereof. In yet another embodiment, the three groups are selected from the group highly halogenated alkyls having 1 to 4 carbon groups, highly halogenated phenyls, and highly halogenated naphthyls and mixtures thereof. By “highly halogenated”, it is meant that at least 50 percent of the hydrogens are replaced by a halogen group selected from fluorine, chlorine and bromine. In yet another embodiment, the neutral stoichiometric activator is a tri-substituted Group 13 compound comprising highly fluorided aryl groups, the groups being highly fluorided phenyl and highly fluorided naphthyl groups.

Illustrative, not limiting examples of ionic ionizing activators include trialkylsubstituted ammonium salts such as triethylammoniumtetraphenylboron, tripropylammoniumtetraphenylboron, tri(n-butyl)ammoniumtetraphenylboron, trimethylammoniumtetra(p-tolyl)boron, trimethylammoniumtetra(o-tolyl)boron, tributylammoniumtetra(pentafluorophenyl)boron, tripropylammoniumtetra(o,p-dimethylphenyl)boron, tributylammoniumtetra(m,m-dimethylphenyl)boron, tributylammoniumtetra(p-tri-fluoromethylphenyl)boron, tributylammoniumtetra(pentafluorophenyl)boron, tri(n-butyl)ammoniumtetra(o-tolyl)boron and the like; N,N-dialkylanilinium salts such as N,N-dimethylaniliniumtetraphenylboron, N,N-diethylaniliniumtetraphenylboron, N,N-2,4,6-pentamethylaniliniumtetraphenylboron and the like; dialkyl ammonium salts such as diisopropylammoniumtetrapentafluorophenylboron, dicyclohexylammoniumtetraphenylboron and the like; triaryl phosphonium salts such as triphenylphosphoniumtetraphenylboron, trimethylphenylphosphoniumtetraphenylboron, tridimethylphenylphosphoniumtetraphenylboron and the like, and their aluminum equivalents.

In yet another embodiment, an alkylaluminum may be used in conjunction with a heterocyclic compound. The ring of the heterocyclic compound may include at least one nitrogen, oxygen, and/or sulfur atom, and includes at least one nitrogen atom in one embodiment. The heterocyclic compound includes 4 or more ring members in one embodiment, and 5 or more ring members in another embodiment.

The heterocyclic compound for use as an activator with an alkylaluminum may be unsubstituted or substituted with one or a combination of substituent groups. Examples of suitable substituents include halogen, alkyl, alkenyl or alkynyl radicals, cycloalkyl radicals, aryl radicals, aryl substituted alkyl radicals, acyl radicals, aroyl radicals, alkoxy radicals, aryloxy radicals, alkylthio radicals, dialkylamino radicals, alkoxycarbonyl radicals, aryloxycarbonyl radicals, carbomoyl radicals, alkyl- or dialkyl-carbamoyl radicals, acyloxy radicals, acylamino radicals, aroylamino radicals, straight, branched or cyclic, alkylene radicals, or any combination thereof. The substituents groups may also be substituted with halogens, particularly fluorine or bromine, or heteroatoms or the like.

Non-limiting examples of hydrocarbon substituents include methyl, ethyl, propyl, butyl, pentyl, hexyl, cyclopentyl, cyclohexyl, benzyl or phenyl groups and the like, including all their isomers, for example tertiary butyl, isopropyl, and the like. Other examples of substituents include fluoromethyl, fluoroethyl, difluoroethyl, iodopropyl, bromohexyl or chlorobenzyl.

In one embodiment, the heterocyclic compound is unsubstituted. In another embodiment one or more positions on the heterocyclic compound are substituted with a halogen atom or a halogen atom containing group, for example a halogenated aryl group. In one embodiment the halogen is selected from the group consisting of chlorine, bromine and fluorine, and selected from the group consisting of fluorine and bromine in another embodiment, and the halogen is fluorine in yet another embodiment.

Non-limiting examples of heterocyclic compounds utilized in the activator of the invention include substituted and unsubstituted pyrroles, imidazoles, pyrazoles, pyrrolines, pyrrolidines, purines, carbazoles, and indoles, phenyl indoles, 2,5,-dimethylpyrroles, 3-pentafluorophenylpyrrole, 4,5,6,7-tetrafluoroindole or 3,4-difluoropyrroles.

In one embodiment, the heterocyclic compound described above is combined with an alkyl aluminum or an alumoxane to yield an activator compound which, upon reaction with a catalyst component, for example a metallocene, produces an active polymerization catalyst. Non-limiting examples of alkylaluminums include trimethylaluminum, triethylaluminum, triisobutylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum, tri-iso-octylaluminum, triphenylaluminum, and combinations thereof.

Other activators include those described in WO 98/07515 such as tris (2,2′, 2″-nonafluorobiphenyl) fluoroaluminate, which is incorporated by reference herein. Combinations of activators are also contemplated by the invention, for example, alumoxanes and ionizing activators in combinations. Other activators include aluminum/boron complexes, perchlorates, periodates and iodates including their hydrates; lithium (2,2′-bisphenyl-ditrimethylsilicate)-4T-HF; silylium salts in combination with a non-coordinating compatible anion. Also, methods of activation such as using radiation, electro-chemical oxidation, and the like are also contemplated as activating methods for the purposes of rendering the neutral metallocene-type catalyst compound or precursor to a metallocene-type cation capable of polymerizing olefins. Other activators or methods for activating a metallocene-type catalyst compound are described in, for example, U.S. Pat. Nos. 5,849,852, 5,859,653 and 5,869,723 and WO 98/32775.

In general, the activator and catalyst component(s) are combined in mole ratios of activator to catalyst component from 1000:1 to 0.1:1 in one embodiment, and from 300:1 to 1:1 in a more particular embodiment, and from 150:1 to 1:1 in yet a more particular embodiment, and from 50:1 to 1:1 in yet a more particular embodiment, and from 10:1 to 0.5:1 in yet a more particular embodiment, and from 3:1 to 0.3:1 in yet a more particular embodiment, wherein a desirable range may include any combination of any upper mole ratio limit with any lower mole ratio limit described herein. When the activator is a cyclic or oligomeric poly(hydrocarbylaluminum oxide) (e.g., “MAO”), the mole ratio of activator to catalyst component ranges from 2:1 to 100,000:1 in one embodiment, and from 10:1 to 10,000:1 in another embodiment, and from 50:1 to 2,000:1 in a more particular embodiment. When the activator is a neutral or ionic ionizing activator such as a boron alkyl and the ionic salt of a boron alkyl, the mole ratio of activator to catalyst component ranges from 0.5:1 to 10:1 in one embodiment, and from 1:1 to 5:1 in yet a more particular embodiment.

More particularly, the molar ratio of Al/metallocene-metal (Al from MAO) ranges from 40 to 500 in one embodiment, ranges from 50 to 400 in another embodiment, ranges from 60 to 300 in yet another embodiment, ranges from 70 to 200 in yet another embodiment, ranges from 80 to 175 in yet another embodiment; and ranges from 90 to 125 in yet another embodiment, wherein a desirable molar ratio of Al(MAO) to metallocene-metal “M” may be any combination of any upper limit with any lower limit described herein.

The activators may or may not be associated with or bound to a support, either in association with the catalyst component (e.g., metallocene) or separate from the catalyst component, such as described by Gregory G. Hlatky, Heterogeneous Single-Site Catalysts for Olefin Polymerization 100(4) CHEMICAL REVIEWS 1347-1374 (2000).

Metallocene catalysts may be supported or unsupported. Typical support materials may include talc, inorganic oxides, clays and clay minerals, ion-exchanged layered compounds, diatomaceous earth compounds, zeolites or a resinous support material, such as a polyolefin.

Specific inorganic oxides include silica, alumina, magnesia, titania and zirconia, for example. The inorganic oxides used as support materials may have an average particle size of from 30 microns to 600 microns, or from 30 microns to 100 microns, a surface area of from 50 m²/g to 1,000 m²/g, or from 100 m²/g to 400 m²/g, a pore volume of from 0.5 cc/g to 3.5 cc/g, or from 0.5 cc/g to 2 cc/g.

Desirable methods for supporting metallocene ionic catalysts are described in U.S. Pat. Nos. 5,643,847; 6,844,480 and 6,228,795, which are incorporated by reference herein. The methods generally include reacting neutral anion precursors that are sufficiently strong Lewis acids with the hydroxyl reactive functionalities present on the silica surface such that the Lewis acid becomes covalently bound.

When the activator for the metallocene supported catalyst composition is a NCA, desirably the NCA is first added to the support composition followed by the addition of the metallocene catalyst. When the activator is MAO, desirably the MAO and metallocene catalyst are dissolved together in solution. The support is then contacted with the MAO/metallocene catalyst solution. Other methods and order of addition will be apparent to those skilled in the art.

In one embodiment the catalyst is a racemic M₂Si(2M-PhInd)₂ZrCl₂ on 0.7/1 MAO on P10 silica, where M is a transition metal selected from Groups 4, 5 or 6; Ph is phenyl; and Ind is indenyl. MAO is, as noted hereinabove, methylalumoxane. Catalysts including racemic M₂Si(2M-4-PhInd)₂ZrCl₂ on 0.7/1 MAO on P10 silica are employed in another embodiment.

Preparation of metallocene catalysts in general may be found described in, for example, U.S. Pat. No. 5,449,651, the disclosure of which is incorporated herein by reference. In general, the silica support material is first impregnated with the activator or cocatalyst, such as methylalumoxane, in the given proportion, with at least half of the activator or co-catalyst being disposed within the internal pore volume of the silica. The silica is then contacted with a dispersion of the metallocene catalyst in a hydrocarbon, desirably aromatic, solvent. The catalyst dispersion and silica which contains the activator or cocatalyst may then be mixed together at a temperature of about 10° C. or less, for a period of time sufficient to enable the metallocene to become reactively supported on the activator/cocatalyst-impregnated silica particles. This mixing time may vary from a few minutes to several hours. The supported catalyst is then recovered from the hydrocarbon solvent and is generally washed. The washing may be done in stages. An aromatic hydrocarbon solvent wash may be done first. Following this, an optional second wash may be carried out with a second aromatic hydrocarbon solvent to remove any unsupported metallocene from the supported catalyst. Finally, a paraffinic hydrocarbon wash may be done to remove remaining aromatic solvent from the supported catalyst. The washing procedures, like the mixing of the metallocene solvent dispersion and activator/cocatalyst-containing silica, are desirably carried out at the relatively low temperature of about 10° C. or less. Following washing the washed catalyst is desirably not dried, with the result that it will contain a substantial residue of the paraffinic hydrocarbon solvent.

Thereafter, the washed catalyst may be dispersed in a viscous mineral oil having a viscosity substantially greater than that of the paraffinic hydrocarbon solvent. Typically, the mineral oil has a viscosity, at 40° C., of at least about 65 centistokes as measured by ASTM D445. In contrast, the viscosity of the paraffinic hydrocarbon solvent is usually less than about 1 centipoise at a temperature of about 10° C. This viscosity difference removes most of the paraffinic hydrocarbon solvent.

The final catalyst dispersion desirably has a significant metal loading measured as weight percent in the dispersion. In one embodiment this metal loading is from about 0.5 to about 6 weight percent. In another embodiment this metal loading is from about 1 to about 3 weight percent, and in still another embodiment this metal loading is about 2 weight percent in the dispersion.

Those skilled in the art will appreciate that a variety of modifications in the above generalized catalyst preparation method may be made without significantly altering the outcome. Therefore, it will be understood that additional description of methods and means of preparing the catalyst are outside of the scope of the invention, and that it is only the identification of metallocenes as catalysts that is necessarily described herein.

It will be kept in mind that the blend is a combination of a metallocene catalyzed propylene random copolymer and a polypropylene homopolymer, and that the homopolymer may be catalyzed using any of the metallocene catalysts described hereinabove, or a conventional Ziegler-Natta catalyst. In some desirable embodiments the blend includes such a Ziegler-Natta catalyzed homopolymer. Ziegler-type polyolefin catalysts, their general methods of making, and subsequent use, are known in the polymerization art.

Conventional Ziegler-Natta catalysts comprise a transition metal compound generally represented by the formula: MR_(x) where M is a transition metal, R is a halogen or a hydrocarboxyl, and x is the valence of the transition metal. Typically, M is a group IVB metal such as titanium, chromium, or vanadium, and R is chlorine, bromine, or an alkoxy group. The transition metal compound is typically supported on an inert solid, e.g., magnesium chloride. Examples of such catalyst systems are provided in U.S. Pat. Nos. 4,107,413; 4,294,721; 4,439,540; 4,114,319; 4,220,554; 4,460,701; 4,562,173; and 5,066,738, which are incorporated herein by reference. Those skilled in the art will be familiar with Ziegler-Natta catalysts and Ziegler-Natta polymerizations in general.

In the case of the homopolymer it is, in one embodiment, characterized as “highly isotactic” because it has a degree of isotacticity of at least about 93 percent, desirably at least about 96 percent by weight. Unless noted to the contrary, the term “iPP homopolymer” includes both pure iPP homopolymers and iPP homopolymers containing less than about 1 weight percent of various alpha olefins (including ethylene) by weight of the homopolymer. One desirable polymer configuration for the random copolymers is the isotactic configuration, with minimal presence of syndiotactic or atactic polymer. Where ethylene is selected as the comonomer, such isotactic C₂-C₃ random copolymers are essentially insoluble in xylene, or have a minimal xylene solubles content, and exhibit a relatively high degree of crystallinity, desirably from about 10 to about 40 percent by weight. In the isotactic polymer configuration C₂-C₃ random copolymers have a degree of isotacticity that is desirably at least about 75 percent, more desirably at least about 93 percent, and most desirably at least about 96 percent. Examples of stereospecific polymer configurations and propagation thereof may be found in U.S. Pat. No. 6,090,325, the disclosure of which is incorporated herein by reference.

It is frequently desirable to mix or otherwise combine certain additives with the PP homopolymer, prior to forming an end use article. Selected additives may be suited to the particular needs or desires of a user or maker, and various combinations of the additives may be used. Because the PP homopolymers are typically produced in the form of pellets or fluff, it is frequently convenient to simply dry blend (for example, via tumble blending) the additives with the pellets or fluff of the two polymers, thereby accomplishing mixing of all components simultaneously. Examples of apparatuses suitable for blending the PP homopolymer base material with an additive include the Henschel™ blender, the Banbury™ mixer, and any other relatively low shear blending equipment. Solution blending may also be done, where the polymers are melted together and the additives are blended with them. Other blending or blending/melting protocols may be employed. Combinations of such equipment may also be effectively used.

Additives that are commonly employed are often combined into commercial additive packages. These packages may include stabilizers, which help to inhibit oxidation or thermal or ultraviolet light degradation of the end use article. Examples of suitable thermal stabilizers include, but are not limited to, pentaerythritol tetrakis; tris(2,4-di-tert-butylphenyl)phosphite; 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-buytl-4-hydroxybenzyl)benzene; octadecyl-3,5-di-tert-butyl-4-hydroxyhydrocinnamate; synthetic hydrotalcite; and combinations thereof. Also frequently employed in such packages are melt stabilizers (also called secondary stabilizers), which help to prevent degradation during melt processing. The melt stabilizers may be selected from a variety of commercially available phosphate inhibitors and die lubricants, including, for example, metal stearates, fluoropolymers, and their combinations.

The amount of additives introduced to the inventive polymer blend may be from about 0.0 percent to about 40.0 percent by weight of the blend. Desirably the amount is from about 0.05 to about 30.0 percent by weight, more desirably from about 0.1 to 10 percent by weight.

In general the processing properties of the blend used in the inventive PP-derived articles of manufacture are improved. These physical properties include, but are not necessarily limited to, the blend's melt flow rate. Processing improvements may also include a relatively high level of activity of the catalyst, particularly for the metallocene catalyst.

For example, catalyst activity is a measure of the grams of polymer produced per hour per gram of transition metal. The activity of some effective metallocene catalysts useful to prepare the homopolymers described herein may range from about 3500 to about 6500 gig/h, at a reaction temperature from about 50 to about 70° C. Fouling is a measure of polymer buildup during the polymerization procedure. It may be measured using a standardized technique from one polymerization run to another and is reported in milligrams of polymer buildup per gram of polymer produced. The fouling level of the described metallocene catalyzed polymerization may range from about 5 to about 25 mg/g.

Another important property is the blend's melt flow rate (MFR). This property may be determined using ASTM D1238, including both procedure A (manual operation) and procedure B (automatically timed flow). The MFR is inversely proportional to the average length of a polymer chain. Thus, a higher MFR value is reflective of a relatively short average polymer chain length. Because the inventive compositions are blends of two main components, which may be prepared individually or together in-situ, the compositions will generally exhibit two distinct MFR's, with the homopolymer usually exhibiting a melt flow rate that is significantly higher than that of the copolymer. Each MFR may range from about 0.4 to about 100 g/10 min, desirably about 0.7 to about 30 g/10 min, using a 2.16 kg load at 230° C.

The term “bonding” as used herein refers to the application of force or pressure to fuse molten or softened fibers together. The term “thermal bonding” is used herein refers to the reheating of staple fibers and the application of force or pressure to effect the a melting (or softening) and fusing of such fibers. Operations that employ drawing and fusing fibers together in a single or simultaneous operation, or prior to any take-up roll (for example, a godet) such as, for example, spunbonding are not consider to be a thermal bonding operation, although the inventive fiber can have the form of or result from a spunbonding operation and similar fiber making operations.

The previously described compositions may be formed into fibers using any suitable melt spinning procedure, such as the conventionally known Fourne fiber spinning procedure known to those skilled in the art of using a Fourne fiber spinning machine. The fiber line can be operated in the fully oriented yarn (FOY) mode in which extruded filaments are first melt drawn and then subsequently mechanically drawn in at least one draw station. In operating the Fourne line in the FOY mode, -polymer is passed from a hopper through a heat exchanger where the polymer pellets are heated to a suitable temperature for extrusion, about 180 to 280° C., and then through a metering pump to a spin extruder. The fiber preforms thus formed are cooled in air, then applied through one or more godets to a spinning role which is operated at a desired spinning rate, typically about 100-1500 meters per minute. The thus-formed filaments are drawn off the spin role to the drawing roller which is operated at a substantially-enhanced speed in order to produce the drawn fiber. The draw speed normally will range from about 1,000 to about 4,000 meters per minute and is operated relative to the spinning godet to provide the desired draw ratio, normally within the range of 1.1 to 5:1. For thermal bonding stable fiber applications, low mechanical draw ratios are generally used. For a further description of suitable fiber-spinning procedures for use in the invention, reference is made to U.S. Pat. Nos. 5,908,594, 5,272,003, and 5,318,734, the disclosures of which are incorporated herein by reference. In particular, the use of certain metallocene catalysts, and particularly isospecific catalysts, may result in structures that may be correlated with desirable fiber characteristics, including strength and toughness.

The fiber line can be operated in the partially oriented yarn (POY) mode in which extruded filaments are melt draw and collected on a high speed winder or similar device. The POY evaluation can be used to simulate the melt drawn characteristics of the melt spinning portion of a spunbond process. In operating the Fourne in the POY mode, polymer is processed similar to the FOY mode except that filament is melt drawn and collected on a high speed winder, up to 6000 meters/min.

Desirably, the POY fibers may exhibit sufficient strength for handling and also may have a relatively high spinnability of from about 2,000 to about 6,000 m/min. Compositions with high POY spinnability rates are highly marketable in the spunbond fiber industry.

A particular advantage of the invention is that the fibers may also be used to prepare thermally bonded non-woven fabrics such as those used for medical gowns and drapes, diapers and other catamenial devices, filters, and the like. These fabrics can be formed by carding thermally bonded staple fiber and thermally bonding such web in a heated calendar roll. Or these fabrics can be formed in a resin to fabric technology, such as the spunbond process.

Fabrics in each case are prepared by thermal bonding at temperatures ranging from about 220 to about 300° C. In one embodiment, the bonding temperature is 240. Particular improvements are seen when the thermal bonding is carried out near the maximum temperatures of a thermal bonding curve. At these temperatures the machine direction tensile strength, in particular, is substantially enhanced by the presence of the designated copolymer, in comparison with non-woven fabrics that are identically prepared but include no proportion of copolymer, i.e., they are only the homopolymer. In some embodiments these fabrics may exhibit a tensile strength, at basis weights of 10 and 17 grams/M² (gsm) and a thermal bonding temperature of about 280° C., that are at least 5 percent higher than those attained in the homopolymer fabric. Particularly at the higher basis weight and same thermal bonding temperature, the tensile strength may be improved, in other embodiments, by at least 10 percent. In still other embodiments, the tensile strength may be improved by 20 percent or more. In addition, the designated copolymer renders a nonwoven with improved hand, softness, or drape. The low atactic polypropylene levels of the designated copolymer results in a composition with low fuming. Compositions with a balance of improved thermal bonded fabric strengths, softness, and good processability offer advantages especially for thermally bonded spunbond applications. Such processes are disclosed in U.S. Pat. Nos. 3,825,379; 4,813,864; 4,405,297; 4,208,366; 4,334,340; 5,652,051; 5,714,256; 5,726,103; 6,224,977; 6,235,664; and 6,482,896, all hereby incorporated by reference.

The invention having been generally described, the following examples are given as particular embodiments of the invention and to demonstrate the practice and advantages thereof. It is understood that the examples are given by way of illustration and are not intended to limit the specification or the claims to follow in any manner.

EXAMPLES Examples 1-6

Fibers are prepared for comparative purposes. They are identified as those prepared from a Ziegler-Natta homopolymer polypropylene alone, having a melt flow rate of 33 g/min [comparative examples, denoted Examples 1 and 2], and those that comprise either (1) 95 percent by weight of the same Ziegler-Natta homopolymer polypropylene and 5 percent by weight of a metallocene catalyzed propylene-ethylene copolymer, wherein the ethylene is present in an amount of about 6 percent by weight of the copolymer [inventive examples, denoted Examples 3 and 4]; or (2) 90 percent by weight of the same Ziegler-Natta homopolymer polypropylene and 10 percent by weight of the metallocene catalyzed propylene-ethylene copolymer [inventive examples, denoted Examples 5 and 6]. The copolymer employed has a melt flow rate of 9 g/min.

The homopolymer resin, and each of the resin blends, are each processed at a melt temperature of 220° C. through a Nordson-design spunbond line fitted with a Hills R&D spunbond die. The processing rate is 0.6 gram/minute/hole. The spunbond line is 1.1 meter in width and is operated in a single beam mode. Attenuation air pressure is slightly adjusted for each resin to produce fiber at the target size of 1.5 denier/filament.

Following fiber preparation, the fibers are thermally bonded at a temperature ranging from 250 to 300° F. to form fabrics at both 10 and 17 grams per square meter (gsm) basis weights. A two inch strip is cut from the fabric made at each condition for purposes of tensile strength and elongation testing in both the machine direction and cross direction.

Tables 1-6 show the results of testing. Tables 1 and 2 show the results for fabrics prepared at 10 and 17 gsm for the polypropylene polymer alone, i.e., Examples 1 and 2, and are thus comparative results. Tables 3 and 4 show the inventive compositions at 10 and 17 gsm, where the copolymer is present in the blend in an amount of 5 weight percent [Examples 3 and 4]. Tables 5 and 6 show another inventive composition at 10 and 17 gsm, where the copolymer is present in the blend in an amount of 10 weight percent [Examples 5 and 6]. TABLE 1 Homopolymer alone* Machine Direction Cross Direction Tensile-max Elongation Tensile-max Elongation Temp lbf % lbf % 250 1.7 25 0.9 25 260 3.3 26 1.0 27 270 2.8 27 1.5 30 280 3.2 30 2.1 41 290 3.7 31 2.4 42 300 4.6 32 2.5 38 *not an example of the invention; at 10 gsm

TABLE 2 Homopolymer alone* Machine Direction Cross Direction Tensile-max Elongation Tensile-max Elongation Temp lbf % lbf % 250 3.3 15 1.6 19 260 4.2 18 2.2 24 5.0 5.0 26 2.4 25 280 6.6 33 3.9 32 290 6.9 38 5.0 45 300 7.7 32 4.9 40 *not an example of the invention; at 17 gsm

TABLE 3 95% homopolymer/5% copolymer blend Machine Direction Cross Direction Tensile-max Elongation Tensile-max Elongation Temp lbf % lbf % 250 2.2 19 1.1 27 260 2.8 27 1.1 27 270 4.0 29 1.6 35 280 4.8 38 1.7 36 290 4.0 37 2.1 40 300 4.8 31 2.5 43 *at 10 gsm

TABLE 4 95% homopolymer/5% copolymer blend* Machine Direction Cross Direction Tensile-max Elongation Tensile-max Elongation Temp lbf % lbf % 250 3.4 17 1.8 26 260 4.3 24 2.0 22 270 4.8 25 2.5 30 280 8.0 40 3.7 36 290 8.5 39 4.6 40 300 8.4 39 4.7 39 *at 17 gsm

TABLE 5 90% homopolymer/10% copolymer blend* Machine Direction Cross Direction Tensile-max Elongation Tensile-max Elongation Temp lbf % lbf % 250 2.4 22 0.9 26 260 2.5 22 1.2 37 270 2.9 27 1.2 29 280 3.5 32 2.2 39 *at 10 gsm

TABLE 6 90% homopolymer/10 percent copolymer blend* Machine Direction Cross Direction Tensile-max Elongation Tensile-max Elongation Temp lbf % lbf % 250 — — — — 260 4.5 21 1.4 22 270 4.7 19 2.3 28 280 8.1 37 4.0 40 *at 17 gsm — indicates no data taken 

1. A fiber, spunbond fabric, or melt blown fabric comprising a polymer composition comprising a resin blend of from about 60 to about 99 weight percent of a Ziegler-Natta or metallocene catalyzed isotactic polypropylene homopolymer, and from about 1 to about 40 weight percent of a metallocene catalyzed propylene copolymer, wherein the copolymer comprises a comonomer in an amount from about 0.05 to about 25 weight percent, based on the copolymer.
 2. The fiber of claim 1 wherein the polypropylene homopolymer is Ziegler-Natta catalyzed.
 3. The fiber of claim 1 wherein the metallocene used to catalyze polymerization of the propylene copolymer is a substituted isospecific CpFlu-type catalyst.
 4. The fiber of claim 1 wherein the metallocene used to catalyze polymerization of the propylene copolymer is racemic Me₂Si(2-Me-4-PhInd)₂ZrCl₂ on 0.7/1 MAO on P10 silica, Ph is phenyl; Ind is indenyl; and MAO is methylalumoxane.
 5. The fiber of claim 1 wherein the comonomer is ethylene and it is present in an amount of from about 1 to about 20 weight percent, based on the copolymer.
 6. An article comprising a fiber of claim
 1. 7. The article of claim 6 wherein the article is a carpet or twine.
 8. The article of claim 6 wherein the article is a staple fiber.
 9. The article of claim 6 wherein the article is a spunbond fabric.
 10. The article of claim 6 wherein the article is a continuous filament.
 11. A thermally bonded non-woven fabric comprising a fiber comprising a polymer composition comprising a resin blend of from about 75 to about 95 weight percent of a Ziegler-Natta or metallocene catalyzed isotactic polypropylene homopolymer, and from about 95 to about 75 weight percent of a metallocene catalyzed polypropylene copolymer, wherein the copolymer comprises a comonomer in an amount from about 0.05 to about 25 weight percent, based on the copolymer.
 12. The fabric of claim 11 wherein the thermal bonding is carried out at a temperature of at least about 240° C.
 13. The fabric of claim 12 wherein the thermal bonding is carried out at a temperature of at least about 250° C.
 14. The fabric of claim 11 wherein the fabric has a machine direction tensile strength that is at least 5 percent higher than the tensile strength of a thermally bonded non-woven fabric made from a fiber that is made from the polypropylene homopolymer alone, the fabrics having basis weights of 10 gsm to 100 gsm.
 15. The fabric of claim 11 wherein the fabric has a machine direction tensile strength that is at least 10 percent higher than the tensile strength of a thermally bonded non-woven made from a fiber that is made from the polypropylene homopolymer alone, the fabrics having a basis weight of 17 gsm.
 16. An article comprising the fabric of claim
 11. 17. The article of claim 11 being selected from the group consisting of baby diaper coverstock, feminine hygiene coverstock, agricultural fabric, housewrap, medical gowns, drapes, and catamenial devices.
 18. A method for preparing a non-woven fabric comprising melt spinning a polymer composition comprising a resin blend of from about 75 to about 95 weight percent of a Ziegler-Natta or metallocene catalyzed isotactic polypropylene homopolymer, and from about 95 to about 75 weight percent of a metallocene catalyzed propylene copolymer, wherein the copolymer comprises a comonomer in an amount from about 0.05 to about 25 weight percent, based on the copolymer, to form a fiber, and thermally bonding the fiber at a temperature of at least about 240° C.
 19. The method of claim 18 wherein the polypropylene homopolymer is Ziegler-Natta catalyzed.
 20. The method of claim 18 wherein the metallocene used to catalyze polymerization of the propylene copolymer is a substituted isospecific CpFlu-type catalyst.
 21. The method of claim 18 wherein the catalyst is racemic Me₂Si(2Me-4-PhInd)₂ZrCl₂ on 0.7/1 MAO on P10 silica; Ph is phenyl; Ind is indenyl; and MAO is methylalumoxane.
 22. The method of claim 16 wherein the comonomer is ethylene, and it is present in an amount of from about 1 to about 10 weight percent, based on the copolymer. 